Thermal shaping of corundum and spinel crystals



Aug. 8, 1950 T F. HART v2,517,661

THERMAL SHAPING 0F CORUNDUM AND SPINEL CRYSTALS Filed March 1, 1946 2Sheets-Sheet l no 1 O l /9 9 1 INVENTOR 7 THOMAS F. HART ATTORNEY Aug.8, 1950 T F. HART 2,517,561

THERMAL SHAPING 0F CORUNDUM AND SPINEL CRYSTALS Filed March 1, 1946 2Sheets-Sheet 2 ATTORNEY Patented Aug. 8, 1 950 I THERMAL SH'AI PIN G OFCORUNDUM'AND'T SPINELlCRYSTALS Thomas Hart,tKenmore, Na: Y.-, .assig'nortel-Thee Linde Air. Products lGompanw-ancorporation:on:

Ohio

Application*Mitrch "1; 194'6,'"Serial No." 651,135-

This invention relats toa -method for forms...

ing small rounded bodies from crystalline corurr dum and-spinel rods,and-especiallyto the fo'rm-a tion' ofsmall gems such as sapphire; rubyand i spinel cabochons,-pendantss and teardrops 5 It-has long beencustomary to-sh'ape spinel crystals and -crystals ofs corundumz such asruby andsapph'ire, bymechanically cutting; grinding; and polishing-themwith abrasivessuchas dia;-- u mond powder. Such'mechanic'al operationsare expensive; slow, and-laborious; and leaveminute scratches onthe-surfaces ofthe crystalss The principal object of: thepresentdnvention is to provide: a" novel method for-forming smallrounded corundum and spinel bodies such 'as ca-- bochons, pendants, andteardrops, which overcomes the disadvantages of mechanical abradingoperations. Otherobjects are to 1 provide: a thermal method for producirigsuch rounded-2; bodies; a method wherein a'small rounded bod-37*- can:be both formed "and severed froma corundum or spinel rod thermally; :anda method whereby a plurality of small rounded bodies'can wbesuccessively formed and severed froma single-crys' tallinecOrundu-m-orspineI rod.

The above and other ob'je'cts',: and-the: novel features of theinvention; willibecome apparent from the following description;havingreference torthe accompanying drawings, wherein:

Fig.. 1. is ris-schematic"elevationa1"viewshowing 'so apparatus -for:performing the preferred embodiment ot the novel thermal method of th'einvenw tion;

- Figuzz is an'ienlarged plan viewof the burner headshownin Fig-.1; J

- Fig.2 3:. is rasectional viewr takenralong the-lines IIIeJII inIFig';2; 1.

Fig.1 4 .is 1. ar' piani view of "a modified form =01 burner head;

. Figs 5 to "11; inclusive; are enlargedside-elevate 40 tional views.showings: successive" stages :in thew formation of a smalli rounded=body 'byrthe pre ferred iembodimentof 'the novelthermal method;

Fig. 12 is a schematicelevational.viewshowinggr apparatus for a forminga: rounded shape on x a crystallinezcorundunr. or spinel: rod byazsecond". embodiment of :the novelathermal method;

Figs 13 to 16, inclusive, are enlarged side.e1eva-; tionals views:showing successive stagesn. in; the: manufacture. of z a corundum;orirspinel' teardrop. from a crystalline corundum .or spinel :rod by."the second embodiment of the novel met-hock;

Figs. 17 .and .18are side and front :elevational-r views;v respectivelyshowing; at cabochon: gem:- formed from the teardrop of Fig. 16; and

and. 12 0 :are side and front-elevational IZSzCIaima-a (Clr49- -84);

.. magnesia-e alummauspinelvis about 21352 C:

. intensitytozmeltstheicorundum or spinel; andidia-i- 2; views;respectively; showing: a; pendantr. genm formediromtheteardrop of=Ei'gw16. The inventioninvolvesdormingxa :bulb: omtheav end of a thinsolid l'unicrystalline: corundunm 0 spinelurod-iby:applying stowanendiportionizthereo i 1-: an intenselyhot. heating:medi-um;v suc'h'asanoxysa natural. gas or oxy-hydrogen fiame', having.=.-sufli Y cientheating intensityotoclheat .theJmaterlal; least superficiallytoritslmeltingt-point; which. sapphirea (alumina). is. abontzx2050iv Ci;andifonr:

face :tensiom causesotheiwmelted material as someaagenerallyisphericallshaper. Theb'ulb themsevered from?theimalmbodyz'ofathearodia ,4 a locality adjacent the baseleofathe.bnlbaanmthec shaping :a-nd:severingxoperationss arexrepeatedu'on thernewlyrexposed-iendzof .therrodx'. It ;is .adua-na! tagieousstoperform:thezseveringrat:leastvpartiallyr by applying toas;selectedicircumferentialzzonesz on therod a heating medium ofsufii'cient heating placing the melted.materialzlfrom itlie zonezbyzthcombined-1:effectsezofl.surfaceetensionrandierosione witha a...h'ot":high velocity gas-streams When flametsuchxaseamoxysnaturalt gas.zflame :is acme ployedi for the .severingaoperationathecburningigasesf-fOfzithQGifiQlIlQiflfit bothztosmeltvandr. displace the;.materialfrom.atheczone. ofrzseverances Thea resultingta-smallr rounded.teardrops shapedtlibcdyr tapers gradually-from-its roundedend::.toza:somes.-. what"pointedibaserandzcarrfurther proc Edi-i tovforma. .cabochon havin .substantiallyrflatt b'asasbyyabradingeoffithepointedebase; ;or.rtoiiormi.- aa; pendant :by; abradingamaterialafronrgthe'lteare dropjn.azlengthwiseldirectionlz.. In the;-;.preferred.embodiment..:lof :thecmethoda, illustratedzin Figs-.11 rtogll;inclusive; a.;crystalliner corundumez 01 551 11161 rod-:1l.:iSiL'lIlOUHtBdfhQriZOBI-ia tall-y atkone end -.in at. chucks; I33rotatedzby's-am electrics-motor 15:1 whilethe -rod il'isyrotatedmml itslongitudinal axis byzthezzmotor, a burner. Hi3; is. held: adjacenttortheefreeaend .ofiithe; I'OdZmETi such .a position-:thata thinribbonzo sheets-likes flame l9 elongated lengthwise oftthegrodiima-'pinges: normally against-ta dengthwiseaextending circumferential-.zonesllflicientlyqto melt .a law; including; the surfaces Flame: I91,is. of such character that the pprti'onssof rodaattbothlends ot-thezone; aresheatedamoreerapidly; and ..tc;,.=a-t greater-depth than.atathermiddlefofr thetzone to- ,form a: bu1b..on-,the=endof:theqrodaand-an ade joining thin .neckmf-t smaller. diametertthamthebulb and .therod.connectingtthe bulb; ,to.;the-re1 mainden. of the rod;b oth...in. one-pcontinuouss; operation. I v

Reterrinea Zol-Figs. :2 and, .3;?,one=;suiteble tyileigot' burner l1comprises a hollow body 2| having a perforated cap 23 threaded over itsopen end. A combustible gas, such as an oxy-natural gas or oxy-hydrogenmixture, is Supplied to body 2| by an inlet 25 connected to a suitablesource of supply (not shown) and flows out through a row of perforationsor ports in cap 23 to produce, when ignited, a plurality of flame jetswhich merge to form a thin ribbon or sheet-like flame elongated in adirection transversely of the individual flame jets and extending thelength of the row.

Proper heat distribution in the ribbon flame l9 and in the heated zoneof the rod is obtained by arranging the gas discharge-ports quite closeto-- gether in a long, narrow, straight double row 21 consisting of twoparallel lines of ports; and by making the ports of such size that theports in the middle part 29 of the row are of relatively small size toprovide flame jets of relatively small size and heating intensity, andthe ports in the two end parts 3i and 33 of the row on both sides of themiddle part 29 are of relatively larger size to provide flame jets ofrelatively larger size and heating intensity. For example, the middlepart 29 may comprise ports of #65 drill size (Manufacturers Standard)and the end parts 3| and 33 may comprise larger portsof #55 drill size.Of course all ports in each part of the row need not be of exactly thesame size, but may be varied in size to some extent to influence theshape of the bulb and adjoining neck produced during the flame formingoperation. Also, the bulb and neck shape can be influenced by varyingthe spacing between the several ports.

, In an alternative type of burner head 35 shown in Fig. 4, the gasdischarge ports are arranged in a long, narrow, straight single row 31to produce a somewhat narrower ribbon flame.

, In both burners l1 and35 the end ports 21a and 31a, which are arrangedfarthest from the end of the rod H, are spaced from their neighbors by agreater distance than is between any of.

the other ports because such spacing has been found to aid in producingthe proper shape of the bulb and to expedite the formation of a, thinneck.

Fig. 5 shows a straight approximately cylindrical rod ll of ruby, havinga diameter of 0.130 inch, for example, which has been selected for theflame forming operation. First, as in Fig. 6, one end of rod II istapered in any suitable way, as by grinding to a cone 381(or frustum ofa cone), advantageously having an included angle of about 45?. The endof the rod H canbe flame shaped without first tapering the end, but amore desirable shape is obtained with the tapered rod. Then the taperedrod H is mounted as in Fig. 1 and the flame forming process is carriedout as previously described herein, by positioning the burner I! about1.125 inches from the rod with the row 21 of ports parallel to the rod.Figs. 7 to 10, inclusive, show the shapes obtained at second intervals,the bulb being indicated at 39 and the adjoining neck at 4|.

"When the desired shape of the bulb 39 is obtained as in Fig. 10, theribbon flame I9 is removed slowly radially 0r laterally from its heatingposition. The bulb 39 ma then be severed from the remainderof the rod IIat the neck 4| in any suitable way, as by mechanically cutting orbreaking the neck portion, or by severing the neck with a flame; Sometypes of ornamental jewelry, however, may require that the rod I I becut at some point on the side of the neck 4| remote from bulb 39.

-When severed at the neck 4|, a generally pear shaped or tear dropshaped body T of the type shown in Fig. 11 is obtained. The remainder ofthe rod I I now has a flame-formed cone 43 on its free end left from theflame shaping operation, and the next teardrop can thus be formed on therod without first grinding the end to a taper. The forming and severingoperations can be repeated on successive end portions of the rod to forma plurality of teardrops without removing the rod from the chuck I3.

In another embodiment of the method, illustrated in Figs. 12 to 16inclusive, a crystalline ruby, sapphire, or spinel rod 45, with orwithout a tapered end, is mounted horizontally at one end in a chuck 41rotated by an electric motor 49. While the rod 45 rotates on itslongitudinal axis, a burner nozzle 5| is held adjacent to the end of therod in such a position that a flame 53 impinges against acircumferential end portion of the rod, desirably substantially normallythereto. It is advantageous to use a multi-jet flame but a single jetflame will operate satisfactorily. As shown in Fig. 13 a generallyspherical bulb 55 of considerably greater diameter than the rod itselfforms by the action of surface tension on material melted by the flame.An operator can control the size of the bulb by regulating the heatingintensity of the flame and the duration of the heating period.

After formation of the bulb 55, and While the rod is still rotating withthe chuck 41, the same high temperature flame 53 is shiftedlongitudinally until it impinges transversely, and desirably radially,against a circumferential zone on under the influence of surface tensionand the dynamic erosive action of the hot gases in the flame, aredisplaced longitudinally of the rod in both directions from the zone ofimpingement of the flame to form a neck or constriction 59. As

- 'illustrated in Fig. 15, the portion of molten corundum which flowedaway from the bulb 55 has formed a second smaller bulb 6! on the mainbody of the rod, and the portion which flowed toward the bulb 55 hasbeen incorporated therewith to produce a pear shape or teardrop form.

Ordinarily, the thermal constricting step is continued until the pearshaped bulb 55 is completely severed from the main body of the rod bythe flame, as shown in Fig. 16. However, severance also can beaccomplished by thermally constricting the rod to a small diameter, asshown in Fig. 15, and then completing the severing operation by forciblybreaking or cutting the neck. In the latter procedure, the thermallyshaped rod of Fig. 15 may be regarded as a blank upon which thefinishing operations can be performed. The rod 45 also may be severed onthe side of the neck 59 remote from the bulb 55 to be used in thiscondition in ornamental jewelry.

After severance of the pear shaped bulb 55, the remainder of the rod 45is left with the second small bulb 6! which tapers to the end of therod. The flame is then applied to the second small bulb 6| on the newlyexposed end of the rotating rod to increase its size, and the resultinglarger The teardrop or pear shaped body T shown in Fig..16, which is theproduct of the method described above, is symmetrical about itslongitudinal axis and has a smooth, clear, scratchi'ree, and glossysurface extremely pleasing in appearance. Such bodies can be used asattractive gems in ornamental jewelry. When a cabochon shape is desired,the teardrop or pear shaped body 'I" of Fig. 16, or T of Fig. 11 istreated by abrasively cutting or grinding off the relatively pointedbase portion until the desired shape is obtained, as by grinding to theplane defined by the line C-C and a normal to the-longitudinal axis ofthe teardrop. Figs. 17 and 18 show a cabochon formed by this methodhaving a' smooth, glossy, scratch-free, clear symmetrical convex surface02- and a plane abraded base63.

When a pendant is desired, the teardrop T'" or T istreated by abrasivelycutting it in alengthwise'dircction and then grinding the plane cutsurface until the desired shape is obtained. Figs. 1 9 and 20 show apendant formed by this method having a smooth, glossy, scratch-free,clear, semipear shaped surface d and a plane abraded side surface 65. 2

Long thin unicrystalline rods of synthetic ruby are frequently shaped bythe method of the invention because of their beautiful red color. Withsuch synthetic ruby rods the body or T should be severed from the rod byeither entirely thermally severing it, or by thermally forming a Verythin neck which can be broken with ease. This is especially importantwhen the ruby rod has a diameter above 0.09.0 inch because such rodsalmost invariably fracture when sawed mechanically. Although ruby rodswhich have been grown in red form are the most practical and readilyavailable raw material, the method of the invention can be applied torods cut from larger bodies such as boules or natural rubies. Likewisethe method is applicable to types of corundum crystals such as syntheticclear unicrystalline sapphire rods, as well as to crystals of spinelsuch as magnesiaalumina spinel.

In an example of the invention a burner of the type shown in Figs. 2 and3 was used with approximately i5 cu. ft/hr. of hydrogen and 17.5 cu.ft./hr. of oxygen, premixed, and flowing through ports of the followingsizes in each line of the row 2'1, reading from left to right in Fig. 2(port sizes are Manufacturers Standard Drill Size numbers): 59, 56, 55,65, 65, 65, 63, 63, 63, 5'7, 55, 55, 55.

The burner was slowly brought into position about 1.125 inches away froma tapered synthetic ruby rod of 0.130 inch diameter with the row 27 ofports parallel to the rod, and the oxy-hydrogen ribbon flame was appliednormally to the rod as it rotated at approximately 75 R. P. M. In about1.5 minutes from the time the burner reached its operating position, a 6x 9 mm. teardrop and a thin adjoining neck had formed, and the burnerwas then slowly withdrawn from its operating position.

In another example of the invention, a single jet oxy-natural gas flameconsuming approximately 12.5 cu. ft./hr. of oxygen and 11 cu. ft./hr. ofnatural gas flowing together through a 0.125 inch inside diameter burnernozzle was applied to the end of a rotating 0.100 inch diametersynthetic ruby rod for approximately 1.25 minutes while maintaining theend of the nozzle 1.25 inches from the rod, and a 0.180 inch diameterball was formed on the end of the rod. Thereafter, the same flame wasshifted and applied 6 radially to forma neck, andthe constricting operation was continued until the diameter of the red, at the zone offlame impingement was reduced. to approximately 0.025 inch. Aftercooling, the resulting teardrop enlargement was manually detached at theneck and its pointed base was mechanically ground off to produce afinished cabochon.

lhe exact mechanism of the process described above is not yetfullyunderstood but the shaping operation is believed to proceed bysurface fusion with consequent reshaping of the mass through the efiectsof surface tension and perhaps flame erosion with, finally,recrystallization.

Specific embodiments of the invention have been described above indetail only by way of illustration. It is to be understood that changesinthe specific procedure and apparatus described, and in the resultingproducts, can be made within the scope of the invention.

I claim:

1. In a method for making a small rounded body from a thin crystallinerod of material selected from the group consisting of corundum andspinel: forming a bulb on such rod by applying against a portion thereofan intensely hot heating medium, while rotating said rod about itslongitudinal axis; and, while rotating said rod about its longitudinalaxis, constricting said rod at a zone adjacent the base of said bulb byapplying against said rod at said zone an intensely hot heating mediumto effect displacement of. said material from. said zone.

2'. Ina method according to claim 1, discontinuing said constricting,step after the formation of a thin neck, and severing said bulb fromsaid rod at said neck.

3. In a method according to claim '1, continuing said constricting stepuntil said bulb separates from said rod.

l. In a. method according to claim 1, during said' constricting stepdisplacing material longitudinally of said rod away from said bulb toform a second bulb on said rod.

5. In a method for making a small rounded body from a, thin crystallinerod of material selected from the group consisting of corundum andspinel: tapering an end of said rod to a reduced diameter; forming abulb on the end of such a rod by applying against a zone thereonadjacent to and including said end an intensely hot heating medium,while rotating said rod about its longitudinal axis; and, while rotatingsaid rod about its longitudinal axis, constricting said rod at a zoneadjacent the base of said bulb by applying against said rod at said zonean intensely hot heating medium to displace material from said zone.

6. In a method for making a small rounded body from a thin crystallinerod of material selected from the group consisting of corundum andspinel: forming a bulb on the end of such a rod by applying against anend portion thereof an intensely hot heating flame; and constrictingsaid rod adjacent the base of said bulb by applying against acircumferential zone on said rod an intensely hot heating flame todisplace material from said zone.

7. A method for making a cabochon from a thin rod of material selectedfrom the group consisting of corundum and spinel comprising forming abulb on the end of such a rod by applying against an end portion thereofan intensely hot longitudinal axis; severing said bulb from said rod,said severing being at least partially accomplished by constricting saidrod at a zone adjacent the base of said bulb by rotating said rod andapplying thereto at said zone an intensely hot heating flame to displacematerial from said zone; and abrading material from the base of saidsevered bulb to form a surface extending transversely thereof.

8. A method for making a pendant from a thin rod of material selectedfrom the group consisting of corundum and spinel comprising forming abulb on the end of such a rod by applying against an end portion thereofan intensely hot heating flame, while rotating said rod about itslongitudinal axis; severing said bulb from said rod, said severing beingat least partially accomplished by constricting said rod at a zoneadjacent the base of said bulb by rotating said rod and applying theretoat said zone an intensely hot heating flame to displace material fromsaid zone; and abrading material from said severed bulb in a directionlongitudinally thereof to form a surface extending in a lengthwisedirection.

9. A method for making small rounded bodies from a thin crystalline rodof material selected from the group consisting of corundum and spinelcomprising forming a bulb on such a rod by applying against an endportion thereof an intensely hot heating medium, while rotating said rodabout its longitudinal axis; severing said bulb from said rod, saidsevering being at least partially accomplished by constricting said rodat a zone adjacent the base of said bulb to form a thin neck by rotatingsaid rod and applying thereagainst at said zone an intensely hot heatingmedium to displace the melted material from said zone; and repeatingsaid forming and severing on successive end portions of said rod.

10. In a process for making a small rounded body from a crystalline rodof material selected from the group consisting of corundum and spinel:forming a bulb and an adjoining thin neck by rotating said rod about itslongitudinal axis while applying to a zone thereon an intensely hotribbon flame arranged lengthwise of said rod, said flame comprising amiddle section of relatively low heating intensity and two end sectionsof relatively high heating intensity.

11. In a process for making a small rounded body from a crystalline rodof material selected from the group consisting of corundum and spinel:forming a bulb and an adjoining thin neck by rotating said rod about itslongitudinal axis while applying to a zone thereon an intensely hotribbon flame comprising a row of flame jets arranged lengthwise of saidrod, the flame jets in the middle part of said row having relativelysmall size and heating intensity, the flame jets on both sides of saidmiddle part of said row having relatively larger size and heatingintensity.

12. In a process for making a small rounded body from a solidcrystalline rod of material selected from the group consisting ofcorundum and spinel: forming a solid bulb on one end of said rod byapplying a flame to a zone on said rod adjacent to and including saidend while rotating said rod about its longitudinal axis; and thereafterconstricting said rod at a zone adjoining the base of said bulb byapplying a flame to said zone to displace material from said zone, whilerotating said rod about its longitudinal axis.

THOMAS P. HART.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 762,183 Agramonte June 7, 19041,967,603 Zimber July 24, 1934 2,235,515 Carpenter Mar. 18, 19412,405,892 Lederer et al Aug. 13, 1946

1. IN A METHOD FOR MAKING A SMALL ROUNDED BODY FROM A THIN CRYSTALLINEROD OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF CORUNDUM ANDSPINEL: FORMING A BULB ON SUCH ROD BY APPLYING AGAINST A PORTION THEREOFAN INTENSELY HOT HEATING MEDIUM, WHILE ROTATING SAID ROD ABOUT ITSLONGITUDINAL AXIS: AND, WHILE ROTATING SAID ROD ABOUT ITS